Adjustable backrests or supports are well known in the art. U.S. Pat. No. 5,112,106 (Asbjornsen et al) discloses a backrest comprising a central spine or rail to which a lumbar support cushion and head cushion are connected via a sliding element. The sliding element is connected to the rail or spine via a ratchet-like connection. The '106 Patent is of interest for teaching the concept of height adjustable lumbar support where the adjusting means is connected to a spine for sliding engagement therewith.
U.S. Pat. No. 2,756,809 (Endresen) discloses a back support comprising a metal sheet with adjustable lumbar and upper-back portions. A screw adjusts the concavity of the upper-back portion while a further screw adjusts the convexity of the lumbar support portion. A pair of cross bars are provided for supporting and securing the lumbar and upper back portions of the sheet to the backrest. The two adjustment screws are mounted on a pair of sliding plates to provide vertical adjustment of the lumbar support area and the upper-back support area. Accordingly, this patent is of interest for teaching independent height and curvature adjustment of the lumbar support and upper-back support portions of a backrest.
Additional references are known which pertain to adjustable back support or backrests, as follows: U.S. Pat. Nos. 2,843,195; 3,241,879; 3,762,769; 4,153,293; 4,452,458; 4,541,670; 4,601,514; 4,632,454; 4,722,569; 4,909,568; 4,915,448; 4,968,093; 5,026,116; and 5,197,780, as well international patent application No. PCT/AU91/00487 (BackCare and Seating Pty. Ltd.).
While the known prior art backrests disclose the provision of lumbar and upper-back support members with independently adjustable curvature and positioning, none of the known prior art teaches the combinations of height adjustment, lumbar height and curvature adjustment, upper-back curvature and position adjustment and side-to-side mobility. The provision of these features in a backrest is important to ensure proper fitting of the backrest for adult bodies of different height and shapes. Furthermore, human beings tend not to be static but like to move or "fine tune" their sitting positions. The known prior art backrests do not provide adequate side-to-side mobility for such movement. Nor do they allow for the convenient minor adjustment of support. In addition, the known prior art back supports are generally bulky or heavy to carry and occupy excessive space at the bottom portions thereof, thereby leaving very little room to sit on a chair.